Abrasive articles generally include a binder material and abrasive grains. Typically, abrasive grains are held to the abrasive article using the binder. There are various classes of abrasive articles that are known in the art including, for example, coated abrasives, structured abrasives, and bonded abrasives. These types of abrasive articles are manufactured by various methods. One method of manufacture includes applying abrasive grains to an uncured or only partially cured binder and then curing the binder. Another method includes mixing abrasive grains with an uncured or only partially cured binder, forming the mixture into abrasive structures or spreading the mixture over a backing, and curing the binder.
Coated abrasives can include a backing, or substrate; a binder; and abrasive grains. Coated abrasive articles can be produced, for example, by coating a backing with a binder precursor, applying abrasive grains, and then curing the binder. Another method of manufacturing coated abrasives includes forming a mixture of binder and abrasive grains, applying the mixture onto a backing, and curing the binder. Some methods of producing coated abrasives include forming multiple layers of binder and/or abrasive grains. For example, a coated abrasive can include a compliant layer, a back coat; a make coat; a size coat; and/or a supersize coat.
Compliant layers and back coats generally refer to initial coatings that are applied to a backing. The compliant layer and/or back coat can be cured prior to application of other coats. A make coat is a layer of binder that has been applied over the backing. In some instances, abrasive grains are applied with the make coat, such as wherein the abrasive grains are blended with the binder prior to application to the backing. Alternatively, abrasive grains can be applied to the make coat after it has been placed over the backing. In the production of some coated abrasives, the make coat is then cured to anchor the abrasive grains in place.
Many coated abrasives also contain an additional binder layer. This layer, called a “size coat,” is typically applied over abrasives grains to complete anchoring of the abrasive grains. In some instances, the size coat is then cured. Some coated abrasives also contain a third binder layer. This layer, called a “supersize coat,” is typically applied over the size coat. The supersize coat can include materials such as, for example, an active filler, an anti-static material, an anti-loading material, or a grinding aid, to enhance the working properties of the abrasive article.
Structured, or engineered, abrasives generally include a backing and an abrasive layer in a pre-configured pattern. One method of forming a structured abrasive includes forming a mixture of abrasive grains and a binder precursor. The mixture is then applied onto a backing such that abrasive structures are formed on the backing. In some applications, the abrasive structures are cured after application of the structures to the backing. Other layers, including size and supersize coats, can be applied over the abrasive structures, with or without intermediate curing.
Bonded abrasives generally include abrasive grains fixed in a binder matrix. In one method of manufacture, a mixture including abrasive grains and a binder precursor is formed into an abrasive tool, for example, an abrasive disc or cylinder, and the tool is cured.
There are several known methods for curing binder precursors. These methods include using visible light, ultraviolet (“UV”) radiation, electron beam radiation, conventional thermal treatment, and combinations thereof. In some instances, a conventional thermal treatment can be used following a primary curing method. For example, a binder precursor can be cured using UV radiation and then conventional thermal treatment can be used to post-cure the binder. Conventional thermal treatments include, for example, baking the binder precursor in ovens. In industrial manufacturing operations, post-curing by conventional thermal treatment can take as long as 4 to 20 hours in large ovens. Long periods of conventional thermal treatment are typically used to avoid thermal shock of the abrasive articles. As a result of long processing times, conventional thermal treatments can have a significant impact on the cost and efficiency of manufacturing abrasive articles. In addition, conventional ovens themselves are large, expensive, and radiate large amounts of heat into the manufacturing environment.
Conventional ovens heat abrasive articles from the outside to the inside and, in order to prevent thermal shock, long ramp-up times are required. This can cause the outer skin of the abrasives to cure and shrink first. Then, as the interior begins to heat up, it can expand and crack or stretch the outer skin. The interior can cure and shrink, creating a stress differential between the highly cross-linked outer skin and the interior region upon cooling. This can lead to deterioration of the binder's physical properties, e.g., elongation and toughness properties. Therefore, it can cause poor adhesion between the binder and abrasive grains, poor product life, and random deep scratches when the product is used.
For example, it is believed that conventional oven treatment can include the following mechanisms:                a. As the oven heats up, the outer skin of the film can be cured first;        b. Since the interior of the film can be less cured, uncured monomer can diffuse to the exterior skin and allow more cross-linking of the exterior skin as opposed to linear network cure;        c. As the interior region heats up, it can expand, thereby stretching and possibly cracking the exterior skin;        d. The interior region can cure and shrink, creating tension stresses in the interior and compression stresses in the outer skin. The interior region may achieve a lower cross-link density than the skin due to lower free monomer content;        e. Upon cooling, differing stresses and differing thermal contraction characteristics of the inner and outer matrices can lead to locked-in stresses or film distortions; and        f. Toughness can be diminished due to surface cracks and surface/interior stresses.It is believed that these mechanisms can lead to significant deterioration of the abrasive article's working properties.        